1. Field of the Invention
The present invention relates to purified protein components of spherons, or racemized protein components of spherons, that are useful for screening compounds capable of preventing and/or ameliorating symptoms associated with cerebral amyloidosis, dementia, or Alzheimer's Disease. The invention also relates to methods of making an Alzheimer's Disease or dementia animal model, the animal model produced therefrom, and to a method of using the animal model to screen for effective Alzheimer's Disease therapies. The invention further relates to methods and compositions that prevent the release of, or reduce the concentration of pro-SAAS protein or fragments thereof, or block, compete with, or attenuate the effects of increased amounts of proSAAS protein or fragments thereof, in the brain.
2. Description of Related Art
Classified under the rubric “amyloidosis” are a number of pathological conditions characterized by the deposition of abnormal fibrils (“amyloid fibrils”) in extracellular spaces. The amyloid fibril, in turn, represents a final common pathway for a diverse array of proteins. Regardless of their biochemical composition, however, all types of amyloid fibrils share (a) a β-pleated sheet structure, (b) green birefringence under polarized light after staining with Congo Red dye, and (c) a fibrillar morphology that has a typical electron-microscopic appearance.
The deposition of amyloid fibrils can affect several organs in the systemic forms of the disorder, exemplified by familial Mediterranean fever, familial amyloid polyneuropathy and systemic amyloidosis, or it can be restricted to one organ in localized forms. Among the latter are conditions classified under the rubric “cerebral amyloidosis,” which covers the Alzheimer group of diseases, namely, Alzheimer's disease (pre-senile dementia, senile dementia); Alzheimer's disease associated with Down' syndrome; Alzheimer's disease associated with other central-nervous-system diseases, such as Parkinson's disorder; and congophilic angiopathy (associated or not associated with Alzheimer's disease). Alzheimer's disease in general is an incurable brain disease affecting middle aged and elderly people throughout the world. According to most recent estimates, it is the fourth or fifth leading cause of death among North Americans, and is responsible for inestimable personal and social tragedy, loss of productivity, and custodial burden to society. There is presently no widely-accepted effective treatment for Alzheimer's disease.
The principle symptom (manifestation) of Alzheimer's disease is the loss of higher mental faculties, typified by the loss of memory and behavior referred to as “dementia.” Dementia is a symptom or syndrome that can be seen in many brain diseases other than Alzheimer's disease, such as stroke, encephalitis and metabolic diseases. Since memory loss and dementia are relatively nonspecific symptoms, a certain and specific definition of Alzheimer's disease is based on the characteristic microscopic state of the brain, described initially by Marinesco, Alzheimer and others. See Alzheimer, A., Allegemeine Zeitschrift fur Psychiatrie 64:146-148 (1907); Marinesco, G., Comptes Rendus des Seances de la Societe de Biologie et ses Filiales 70:606-608 (1911).
The particular microscopic features that are accepted indicators of Alzheimer's disease, and that separate Alzheimer's disease from other causes of dementia, are the accumulation of large numbers of brain lesions referred to as senile or amyloid plaques and neurofibrillary tangles. Senile or amyloid plaques are spherical, ranging from 10 to 200 μm in diameter, and while found only occasionally in aged adult cerebral cortex, are found in large numbers in Alzheimer-affected cortex. These lesions, when found in suitable quantity in a brain sample, are the definitive criteria for the diagnosis of Alzheimer's disease.
Amyloid plaques in large quantities are essentially found only in the Alzheimer group of diseases, whereas neurofibrillary tangles are nonspecific and are found in at least ten other neurological diseases. See Corsellis, J. A. N., GREENFIELD's NEUROPATHOLOGY 951-1025 (4th ed. 1984) (Edward Arnold, London). Individual amyloid plaques have roughly 1000× the volume of individual neurofibrillary tangles. True measurements of total brain amyloid plaque and neurofibrillary content are not available, but on the above basis it is likely that the volume of abnormal brain tissue occupied by amyloid plaques is many hundreds of times that of neurofibrillary tangles. The essential feature of the amyloid plaque is the presence of amyloid fibrils, which are a congophilic red-green birefringent microfibrillar material. Corsellis, loc. cit.
A microscopic structure referred to as the dense microsphere (DMS) is known to exist in normal brain and in brain affected by Alzheimer's disease. See Averback, Acta Neuropathol. 61:148-52 (1983); results confirmed by Hara, J. Neuropath. Exp. Neurol. 45(2):169-178 (1986). The DMS more recently have been called “spherons.” “Spherons” in the context of the present invention therefore will denote the same thing as DMS, and refer to the spherical microscopic structure that exists in normal brain.
Some specialists believe that spherons are linked to cerebral amyloid plaques as the source of, or as a precursor to, the cerebral amyloid characteristic of Alzheimer's disease and related conditions. Evidence for the existence of spherons comes from microscopic histological section studies of fixed whole brain tissue. The spherons are observed as randomly dispersed, highly infrequent structures numbering ˜102/mm3.
Various components of spherons (e.g., “DMS”) have previously been identified. It is known that the disintegration of spherons in the brain parenchyma is associated with the onset and progression of cerebral amyloid plaque formation that is characteristic of Alzheimer's disease and related conditions. More specifically, disintegration of spherons releases protein and non-protein components, or mixtures of protein and non-protein components. A portion of the spheron components form cerebral amyloid plaques, while other portions either remain in the brain, or are removed from the brain parenchyma via circulating bodily fluids, including cerebrospinal fluid, serum and the like.
It also is believed that spherons undergo a growth and bursting cycle bringing about a cataclysmic cascade of spheron bursts, and subsequent brain injury. As disclosed in U.S. Pat. No. 6,130,221, the disclosure of which is incorporated by reference herein in its entirety, an important mechanism of initiation and promotion of spheron disruption has been discovered that involves a distinctive autocatalytic phenomenon, whereby the disruption, degeneration, and evolution of an individual spheron into an individual cerebral amyloid plaque provides the stimulus for a group or field of other spherons to disrupt, degenerate and evolve in a recurring set of waves. This unchecked, autocatalytic phenomenon causes an exponential growth pattern: small, perhaps statistically insignificant differences (between individual brains) in starting numbers of disrupted spherons in situ evolve into statistically significant differences after generations of the cycle. For example, if all other factors were equal, a subject having an initial group of 100 spheron bursts would not be statistically or symptomatically different from a second subject having an initial group of 98 spheron bursts. However, if over time each of the initial spheron initiated 10 subsequent spherons to disrupt, each of which in turn initiated 10 subsequent spheron disruptions, then group 1 after 20 generations would have 2×1020 more disrupted spherons than group 2, which is significant.
The description herein of any disadvantages of known compounds, systems, methods and apparatus is in no way intended to limit the present invention. Indeed, the present invention may employ one or more known compounds, systems, methods, and apparatus without suffering from the known disadvantages.